1. Field of the Invention
This invention relates to digital electronic watches, and more particularly to a digital watch having power selection circuitry for the oscillator and initial divider, which supplies power from only one battery when the battery voltage is high (current is low) and which supplies power from two series batteries when the battery voltage is low (current is high).
2. Description of the Prior Art
In the art, the LED digital watch and the liquid crystal display digital watch with an illumination light have employed two batteries (each supplying 1.5 volts) and a series resistor to power their oscillator/divider. Use of two batteries wasted power, i.e., only one battery, 1.5 volts, was needed when in the case of the LED digital watch, the LED display elements were not illuminated and in the case of the liquid crystal display digital watch when the illumination light was not lit. Such digital watches have been disclosed in application Ser. No. 515,797, filed Oct. 17, 1974, entitled "Digital Watch with Liquid Crystal Display," in patent application Ser. No. 558,183, filed Mar. 13, 1975, entitled "Digital Watch with Liquid Crystal and Light Emitting Diode Display" both of which are commonly assigned. The subject matter of these cross-references are incorporated herein in their entirety. A drawback with these digital watches is that two betteries and a resistor connected in series are being used to supply voltage to the oscillator/divider all of the time when the voltage from only one battery would be sufficient most of the time. This technique was used because one battery alone with a high load current only put out 1.2 V, which was so low that requiring operation at that voltage caused very low production yields. In order that 1.5 V be supplied during the short time that current was high, about 2.0 V was supplied the rest of the time. Current increases faster than supply voltage, so power was wasted by running at such a high voltage.